This application claims the priority of application Ser. No. 102 45 035.8, filed Sep. 26, 2002, in Germany, the disclosure of which is expressly incorporated by reference therein.
The present invention relates to vehicles which have an all-wheel drive with a fixed torque distribution and a controllable longitudinal lock with or without a controllable main-axle lateral lock.
In the case of vehicles having a locking torque at the longitudinal and/or lateral lock, an understeering of the vehicle may occur in certain driving situations as a result of the torque distribution between the front axle and the rear axle and the coefficient-of-friction conditions at the wheels. As a result the vehicle will no longer follow the driving direction desired by the driver and will lurch by way of the front wheels.
The present invention uses a recognized correlation between the vehicle speed, the lateral acceleration and the steering angle for optimal controlling of the lateral acceleration. The method according to the invention has the advantage that, in the event of an understeering, the vehicle handling can be influenced by a change of the torque distribution between the axles and/or the reduction of the locking torque at the lateral lock. It is particularly advantageous that, through the use of the lateral acceleration and the driving speed in a three-dimensional characteristic diagram, an envelope curve for the pertaining steering angles can be stored. As a result, the corresponding steering angle at which the vehicle allows a neutral vehicle handling can be determined for any driving situation. The present invention therefore has the advantage that, when the steering angle deviates from the envelope curve, an unstable driving condition is detected, in which case an understeering of the vehicle is recognized when the actual steering angle is defined to be greater than that of the envelope curve. If the steering angle is within the envelope curve, a normal driving situation exists and the vehicle follows the driving direction desired by the driver. When determining the driving situation, a plurality of parameters, such as the yaw angle, the yaw velocity, the yaw acceleration, the driving speed or also replacement models for the rotational wheel speeds can be included. Finally, quantities which influence the vehicle handling determined in the application, may be evaluated and may be filed as information in the control unit of the vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.